Magnetically operated two position electrical indicator

ABSTRACT

An indicator to show either of two conditions of an electrical circuit and including an electromagnetic structure with poles and coil means to energize the poles alternatively to either magnetic polarity, and also including a permanently magnetized armature with indicia thereon, either directly or on an attached member, the electromagnetic structure and armature with indicia being included within a housing that has at least one window through which the indicia may be seen to indicate whether the armature is in one or the other of two end positions determined by the current in the coil in response to the external circuit. The poles of the electromagnet may cooperate with the permanently magnetized armature to hold the latter in either of the end positions while allowing easy transfer to the other end position when current flow is reversed.

United States Patent William A. Knecht RFD #2, New Hartford, Conn. 06057 [21] Appl. No. 655,641

[22] Filed July 24, 1967 [45] Patented Apr. 6, 1971 Continuation-impart of application Ser. No. 570,937, Sept. 8, 1966, now abandoned.

[72] lnventor [54] MAGNETICALLY OPERATED TWO POSITION ELECTRICAL INDICATOR 35 Claims, 17 Drawing Figs.

[52] US. Cl 340/373, 340/366, 340/378 [51] Int. Cl G08b 5/14, G08b 5/22 [50] Field of Search 340/373, 378, 366

[56] References Cited UNITED STATES PATENTS 3,210,758 10/1965 Huston 340/373 2,740,956 4/1956 Hatton 340/373 2,866,965 12/1958 l-loudek, Jr. 340/378 3,026,512 3/1962 Baker 340/373 3,140,431 7/1964 Schalkwijk 340/373X Primary Examiner-Harold l. Pitts Attorney-Donald P. Gillette ABSTRACT: An indicator to show either of two conditions of an electrical circuit and including an electromagnetic structure with poles and coil means to energize the poles alternatively to either magnetic polarity, and also including a permanently magnetized armature with indicia thereon, either directly or on an attached member, the electromagnetic structure and armature with indicia being included within a housing that has at least one window through which the indicia may be seen to indicate whether the armature is in one or the other of two end positions determined by the current in the coil in response to the external circuit. The poles of the electromagnet may cooperate with the permanently magnetized armature to hold the latter in either of the end positions while allowing easy transfer to the other end position when current flow is reversed.

PATENIED APR 6 IENI sum 1 or 4 INVENTOR WILLIAM KN ECHT ATTORNEY PATENTEDAPR 6197! 3,573,811

SHEET 2 BF 4 C r I- W JnRIILI II I FPI llllLlllll l ll'lll INVENTOR WILLIAM KNECHT mm ATTORNEY PATENTEU APR 6197i 3,573,811

SHEET 3 [IF 4 FIG. 10

INVENTOR 4 WILLIAM KNECHT 1 MAGNETICALLY OPERATED TWO POSITION ELECTRIC AL INDICATOR This is a continuati'on-in-part of my copending application Ser. No. 570,937 filed Aug. 8, 1966 and now abandoned.

This invention relates to a magnetically operated indicator capable of being made in microminiature size and having means to connect to an electric circuit to produce a visual indication of selected operating conditions in the circuit.

Because of the increasing complexity of electrical and electronic equipment, the apparatus is frequently divided into modular units each of which can be removed and replaced independently of the others. This applies particularly to socalled integrated circuits in which each module may be a relatively complex circuit printed on a card or other substrate. This removal and replacement may be done at a central loca tion or, particularly in the case of equipment intended for military operation, it may be done at the point of operation. In either case, and particularly in the latter, it is desirable, if not essential, that any fault in the operation be easily detected and preferably be self-indicating.

As a result there has been established a requirement for a type of indicating unit which must be extremely small, inexpensive, as nearly foolproof as possible, and capable of giving unambiguous indications of malfunction of the apparatus to which it is connected with little or no continuous current drain. The indicator of the present invention meets all of these criteria in a bistable electromechanical device having at least one colored flag or indicating member capable of being positioned in either of two locations, one of which indicates faulty operation of the equipment to which the device is connected and the other of which indicates proper operation. The indicator member is mechanically connected to a permanent magnet which is pivotally mounted adjacent to two ferromagnetically soft pole pieces magnetically energized by a coil structure that may include one or more coils. The two possible positions of the indicator members correspond to a net current flow in the coil structure in the two possible directions of such flow, but because of the permanent magnetic field of the armature that operates the indicator member, the indicator member can be held in either position by the magnetomotive force of the armature in the absence of any current in the coil structure. As a result the current required to change the position of the indicator member from one of its positions to the other need not be continued after a change in position has taken place and therefore it is unnecessary to provide a continued operating current in order to maintain a continued indication of either faulty or proper operation. This is important because it reduces the current drain on the equipment, which could be a significant factor in the case of equipment having a large number of indicators.

The indicator may be controlled by applying current pulses to the coil structure whenever necessary to change the position of the indicating member, or it may be controlled by connecting the indicator to a voltage source capable of maintaining a continuous current flow in the coil structure. In the latter case the indicator preferably includes switching means to disconnect the coil structure from the voltage source as soon as the indicating member has moved to its alternative position, the switch means being so arranged as to establish a new path of conduction through the coil structure to produce a magnetomotive force capable of causing the indicating member to return to the'first position if the operating condition of the equipment to which theindicator is connected warrants such return.

The invention will be further described in connection with the drawings in which:

FIG. 1 is a plan view, partly in cross section, of one embodiment of an indicator constructed according to the invention;

FIG. 2 is a side cross-sectional view of the indicator of FIG. 1;

FIG. 3 is an end view of the indicator of FIG. 1;

FIG. 4 is a schematic diagram of an actuator circuit suitable for use in the indicator of FIG. 1;

FIG. 5 shows a cross-sectional view of a modified indicator similar to that of FIG. I;

FIG. 6 shows a cross-sectional view of another embodiment of the invention;

FIG. 7 is a plan view of the embodiment of FIG. 6 with part of the structure broken away to show the interior construction;

FIGS. 8 and 9 are side and plan views of the modified switch constructed in accordance with the invention;

FIGS. l0I5 show modified forms of stator pole and armature arrangements in accordance with the invention; and

FIGS. 16 and 17 show another modification of the inven- -tion.

The indicator of FIG. 1 comprises a base 21 on which are mounted two coils 22 and 23. A soft steel core 24, or other form of ferromagnetically soft material, extends through the coils 22 and 23 and is tightly magnetically connected to two ferromagnetically soft pole pieces 26 and 27 at its outer ends. These pole pieces are bent around a barrier 28 and the outer ends of the pole pieces, indicated by reference characters 26a and 27a, extend substantially parallel to each other and in the same direction.

A shaft 29 mounted perpendicularly to the base 21 and pivotally supports a magnet 31 having opposite ends 31N and 315. The magnet is of a type having high retentivity so that it remains permanently magnetized with a north pole at the end 3IN and a south pole at the end 318. The end 31N is formed by two surfaces 31a and 31b that converge to a more or less sharp wedge shape while the end 318 is similarly defined by two surfaces 310 and 31d that also converge at a wedge shape, and in such a way that the edge 31b is substantially parallel to the surface 31c and the surface 31a is substantially parallel to the surface 31d. Moreover, for best magnetic circuit operation, the surfaces 31a and 31d should be substantially parallel to the ends 26a and 27a, respectively, of the pole pieces 26 and 27 when the magnet 31 is in the position shown in FIG. 1. This position of the magnet 31 is one of its two end, or limiting, positions. Arbitrarily, this position is defined as the malfunction position, that is, the position in which the indicator warns that the circuit to which it is connected is not functioning correctly. The other end position, called the functioning position, would be with the surfaces 31b and 310 substantially parallel to the ends 27a and 26a respectively.

Attached to the magnet 31 is a disc-shaped, nonmagnetic indicating member 32 having a downwardly-turned edge 32a. The downwardly-turned edge 320 extends over an arc of about and the magnet 31 is so oriented with respect to this downwardly-turned edge 320 that the end 31N points substantially directly to the center of the edge 320. To assist in maintaining correct orientation of the indicating member 32 with respect to the magnet 31, two tabs 32b and 320 are bent downwardly from the member 32 at points opposite the edge 320. These tabs 32a and 320 not only maintain the orientation of the magnet by lying adjacent to the surfaces 31c and 31d, but they also act as stops to keep the surfaces 31c and 31d from actually coming into contact with the ends 26a and 27a of the pole pieces and sticking to the pole pieces 26 and 27 in either of the end positions of the magnet.

The indicator also includes switch means in the form of a pair of switches, the first of which has a movable actuator arm 33 and a relatively stationary post 34 attached to the base 21. The arm 33 may be affixed to the barrier 28, which is also preferably of insulating material, and it may also be soldered, welded, or otherwise connected to a pad 30. The other switch comprises a movable am 36, which may be anchored to a pad 35 and located by the barrier 18, and a relatively stationary contact post 37 mounted on the base 21. Both of the movable arms 33 and 36 are resiliently biased toward their respective contact positions 34 and 37 so that in the absence of obstruction, both of the switches would be nonnally closed.

One form of obstruction to force the movable arms 33 and 36 away from their fixed contact positions 34 and 37 consists of the sides 32d and 322 of the downwardlytumed edge 320. In the position shown in FIG. 1, the side 32d is pushed against the movable arm 33 to separate it from its contact post 34, thus opening this switch. The location of the other side 32c is such that when the magnet 31 is in its other position, the side 32:: presses against the movable arm 36 and forces it away from the post 37 while at the same time the side 32d moves away from the movable arm 33 and allows the latter to return to its normal contact with the post 34.

At the other end of the indicator are four terminals 40-43, and around the periphery of the base 21 are four walls 44-47 that form part of the enclosure for the indicator. Three of these walls 44-46 may be opaque, while the fourth wall 47 has a transparent window portion 47a. In actual fact, all of the walls 44-47 may be made of transparent plastic most of which has been rendered opaque by the layer of paint except for the area of the window 47a.

FIG. 2 showsa side view of the indicator of FIG. 1. The pole piece 27 extends from the end of the coil 23 where it is attached to the end of core 24 out past the barrier 28 to the region of the magnet 31 although the end 27a of the pole piece has been broken away to permit the magnet to be seen. The magnet is here shown pivotally supported on a stud 29 affixed to the base 21 with a retaining collar 48 to limit end play.

The movable arm 36 of the switch is, in this embodiment, divided into two thin resilient members 36a and 36b, one of which may be thicker or longer than the other so as to have a different resonant frequency The purpose of different resonant frequencies for the two members 36a and 36b is to increase the chances that at least one of them will at all times be in contact with the post 37 when the surface 32e is not pressing against the members 360 and 36b.

Beneath the magnet 31 and the pole pieces 26 and 27 and between the arms 33 and 36 is a small space within which may be located an electronic circuit package 53 capable of controlling operation of the indicator. The lower part of the barrier 28 may be a socket into which the circuit package may be plugged. An extension 28a of the barrier 28 may be provided to hold the circuit package in place.

FIG. 3 shows an end view of the indicator and illustrates the position of the window 47a in the wall 47 and with respect to the downwardly-tumed edge 32a of the indicating member.

Part of the wall 47 hasbeen broken away to illustrate that the downwardly-tamed edge 32a has been divided into two sections 32a and 32a" which are painted different colors. When the magnet 31 is in the position shown in FIG. 1, the section 32a is in front of the window 470 and the color of the section 32a" is therefore visible through the window. It has been arbitrarily stated that this position indicates malfunction of the electrical equipment to which the indicator is attached. When the magnet 31 is in its other end position, the color, or other indicia, of the section 320 fills the window 47a and affords a clear indication that the equipment to which the indicator is connected is functioning correctly. Instead of using the window in the end wall 47 of the indicator, a window may be placed in an upper wall 49 through which the flat surface of the indicating member 32 may be viewed. The wall 49 is indicated in FIGS. 2 and 3 but has been removed in the crosssectional view in FIG. 1. However, the position of the transparent window may be indicated in FIG. 1 by the position of a circle 49a, and the surface of the indicating member 32 may have a sector 32f painted a different color than the remainder of the surface to be visible through the window 49a only when the indicating member 32 is in the position shown.

FIG. 4 shows a typical schematic diagram of the electronic circuit 53 of FIG. 2. As may be seen, there are connections from this circuit to the coils 22 and 23 and to the terminals 40- -43. The circuit comprises three transistors 56-58 of which the'emitter-collector circuits of the transistors 56 and 58 are connected in series with the coils 22 and 23 and the switch arms 33 and 36. The two posts 34 and 37 are connected together to the terminal 43 which in turn is connected to the positive terminal of a source of operating voltage for the circuit. In the present embodiment this voltage source is a 28- volt DC supply. Two diodes 59 and 60 are connected directly in parallel with the coils 22 and 23 to suppress inductive surges and to minimize radio frequency noise that might be generated in the circuit. The junction between the diode 59 and the coil 22 is connected to the collector of the transistor 56, the emitter of which is connected to the ground terminal 41. The emitter of the transistor 58 is also connected to ground and its collector to the coil 23. A resistor 62 connects the base of the transistor 56 to the terminal 42, which in turn is connected to a positive bias voltage of about 4 volts, while the bases of the transistors 57 and 58 are connected by means of two resistors 63 and 64 to the terminal 40 which receives an input voltage that governs the operation of the circuit and therefore the operation of the indicator.

The circuit is so arranged that as long as the equipment to which it is connected is functioning properly, a voltage not greater than approximately +0.25 volt will be applied to the terminal 40 relative to the ground terminal 41, but as long as the equipment is malfunctioning, a voltage of at least +3.6 volts will be applied to the terminal 40. Let it be assumed that the indicator is in the position shown in FIG. 1, which corresponds to an indication of malfunctioning of the equipment to which it is connected. In that condition, the am 36 will be in contact with the post 37 but no current will flow through the coil 22 because the transistor 56 will be nonconductive.

Now if it is assumed that the equipment being tested returns to a proper functioning state, the voltage applied to the terminal 40 will be reduced to 025 volts or less and this will bias the transistor 57 to the nonconductive state so that no current will be drawn through the resistor 62. Thus the voltage at the base of the transistor 56 will rise to a value of approximately +4 volts which will render the transistor 56 conductive and make it possible for current to flow from the terminal 43 through the post 37, the arm 36, the coil 22 and emitter-collector circuit of the transistor 56. Current flowing in the coil 22 will cause the pole piece 26 to assume a north magnetic polarity and the pole piece 27 to assume a south magnetic polarity which, as shown in FIG. 1, will cause the magnet 31 to flip to the reverse position breaking the connection between the arm 36 and the post 37 and at the same time pennitting the arm 33 to contact the post 34. However, the coil 23 will draw no current because the transistor 58 is biased to a nonconductive state by the near-zero voltage applied to the terminal 40 during the proper functioning of the equipment.

If the equipment under test again begins to malfunction, a voltage of at least approximately +3.6 volts will be applied to the terminal 40, which will bias both the transistors 57 and 58 to the conductive state and permit current to flow through the transistor 58 and the coil 23, reversing the previous magnetic polarity of the pole pieces 26 and 27 to drive the magnet 31 back to the position shown in FlG.'1. This breaks the connection between the arm 33 and the post 34 and deenergizes the coil 23 but by that time the permanent magnet 31 is in position to hold the indicator 32 in the position shown in FIG. I. At the same time conduction of the transistor 57 causes a current to flow through the resistor 62 which so reduces the voltage at the base of the transistor 56 that the latter cannot become conductive even though its collector is now connected via the coil 22, the arm 36, and the post 37 to the supply voltage applied to the terminal 43.

Because the switches connected in series with the coils 22 and 23 are arranged so that each of these switches will be opened by movement of either the arm 33 or the arm 36 very shortly after the coil 23 or 22, respectively, has been energized, the flow of current through the coils will be self-terminating, which is very advantageous in keeping the power consumption of the indicator as low as possible.

On the other hand, the switches can be eliminated entirely and the coils 22 and 23 directly connected to the terminal 43 if the resultant drain on the power supply can be tolerated. Minimum energy consumption can still be obtained without having the switches connected in series with the coils 22 and 23, if, in addition, the transistor 57 and the resistors 62-64 are eliminated and the transistors 56 and 58 are controlled directly by logic pulses of the proper amplitude applied to their bases in such a way that only one of the transistors 56 and 58 can become conductive at a time.

Moreover, the electronic circuit package 53 need not be included in the indicator itself but the terminals of the coils 22 and 23 can be controlled by properly applied driving voltages from outside the indicator. The coils 22 and 23 can even be combined into a single coil with a bifilar winding or, by using a standard double-poledouble-throw current-reversing switch, the two windings of the coils may be combined into a single two-terminal winding. Essentially what is required is that the poles 36 and 37 be magnetically energized by a net fiow of current in one direction or the other in the energizing coil or coils, whether this current is produced by connecting two terminals of a single coil to a voltage source, first in one polarity and then in the other, or whether it is produced by energizing one or the other of two coils, or whether it is produced by energizing both coils simultaneously but one more than the other to achieve a net current, and hence a net magnetic field, in one direction.

FIG. 5 shows an indicator similar to that of FIG. 1 but with modifications in the magnetic circuit components and in the indicating member. However, many of the parts are identical with those in FIG. 1 and are identified by the same reference numerals. These include the coils 22 and 23, which, when energized by an electric current, provide the required magnetic flux to operate the indicator.

The pole pieces that channel this flux are somewhat differently shaped than those in FIG. I and are designated by reference numerals 126 and 127. The main difference between these and the pole pieces 26 and 27 is that the outer ends 126a and 1270 of the pole pieces in FIG. 5 have an extra offset that brings them closer together. The pole pieces 126 and 127 are bent inwardly around the barrier 28 to form sections 126b and 127b, but instead of extending straight from that point, are bent inwardly a second time around the extension 28a to form the sections 126a and 1270 that are closer together than the sections 26a and 27a in FIG. 1. This is permissible because, instead of the stops 32b and 320 to keep the indicator member aligned with the magnet and to keep the surface of the magnet from actually touching the pole pieces, the structure in FIG. 5 has only a set of insulating tapes 66- -69 on the faces 31 a31d of magnet. Even these tapes may be eliminated by making the included angles between the surfaces 31a and 31b and between the surfaces 310 and 31d slightly greater than the total angle through which the magnet 31 pivots between its two extreme positions so that the extreme tips of the magnet ends 31N and 318 do not strike the pole pieces.

The magnet material must be chosen not only to retain its magnetization but also to have relative low reluctance to form a low reluctance path between the pole pieces. One satisfactory material for the magnet 31 is 18 percent cobalt steel, which has the desired magnetic properties and is also relatively easy to shape.

The folded over edge of the indicating member 132 is not cylindrical in the embodiment in FIG. 5 but is divided into two relatively flat surfaces 132' and 132" at an obtuse angle to each other. This presents a clearer image in the window 470 to make the indication somewhat more definite than the rounded edge 32a in the FIG. 1.

Finally, the outer ends 1330 and 1360 of the resilient arms I33 and 136 are bent slightly outwardly to present a better impact angle to the abutment surfaces 132d and l32e. This angle, together with the lack 'of rounding of the downwardly extending edge 132a, helps to keep the abutment surfaces from jamming or wedging behind the arms 133 and 136.

FIG. 6 is a modified embodiment of the invention adapted for mounting in a cylindrical container instead of a boxlike one. The magnetic components are the same as in the embodiment of FIG. 5 and therefore need not be described again.

These components are mounted in a cylindrical case 71 which may either be made of plastic or of a nonmagnetic metal and which has an inner shelf 72 anda face plate 73. The indicating mechanism includes an actuating member 74 attached to the armature 31 to pivot therewith. At the end of the poles 126a and 127a is a support member on which is mounted a bearing 77. A short shaft 78 is pivotally held within the bearing 77 and supports a disc 79. The disc 79 has a radial slot formed in it by means of two-downwardly-turned edges 81 and 82 and the free end of the actuating member 74 engages the edges of the slot so that as the armature 31 pivots back and forth the actuating member 74 will pivot the disc 79 back and forth.

As may be seen in FIG. 7, the disc 79 has a segment 84 painted a different color than the remainder of the disc to be visible'through a window 86 when the actuating member 74 is pivoted to the opposite position from that in which it is shown in the drawing. In this way, since the actuating member is radially spaced from the center of the shaft 78, pivotal movement of the armature and the actuator member 74 about the axis of the armature will cause a corresponding pivotal movement of the disc 79 about an axis perpendicular to the axis of the armature.

FIGS. 8 and 9 show a different form of switch arrangement for use with the magnetic components of the invention as described in the embodiment of FIG. l3, or FIG. 5. Whereas the embodiment described hereinabove utilizes the indicating member merely as a mechanical actuator for the switches, the embodiment in FIGS. 8 and 9 uses the indicating member, here identified by reference characters 232, as one of the electrical components of the switches. As shown in FIG. 8, the switch includes arms 87-89 to press against the surface of the indicating member 232. The latter is made of a nonconv ductive material, and, as shown in FIG. 9, has two conductive areas 91 and 92 printed on the surface connected by the switch arms 87 -89. These arms are so placed that the arm 89 always bears against the conductive area 92 whereas the arms 87 and 88 alternately bear against the conductive areas 91 and 92. When, as is indicated in FIG. 9, the am rests against the conductive area 92, there is a short circuit between that arm and the arm 89. By connecting the arm 89 to the source of supply voltage and the arm 88 to the coil 23, here indicated only diagrammatically, and by connecting a battery 93 between the arm 89 and the centertap that joins both the coils 22 and 23, the coil 23 will be energized, or, more properly speaking, will be energizable, when a further switch 94 is closed. The closing of the switch 94 would, in accordance with the purpose of the invention, be controlled by the electrical apparatus that is being monitored, and when the switch 94 is closed the magnetic field produced by the coil 23 will cause the indicating member 232 to swing, or pivot, to its other end position in which the conductive area 92 would short circuit the arm 87 to the arm 89 and'the am 88 would no longer be resting on the area 92 but would, instead, be resting on the area 91. When the arm 87 is short circuited to the arm 89, the coil 22 may be connected to the battery 93 provided a further switch 96 is closed by the circuit that controls the operation of the indicator. One of the problems in the indicator of the present invention is to reach a proper balance between the holding force that maintains the armature in either of its two limiting positions and the force required to shift the armature out of that position and into the other end position. The magnetic circuit is most efficient when there is a broad area of contact between the armature and the poles, but in such a case the armature would tend to stick to the poles even when the 7 reverse current is applied to the coils.

FIGS. 10-15 show various pole and armature arrangements to minimize the sticking and yet retainas much as possible of the holding force. The poles 326 and 327 in FIG. 10 cooperating with the armature 31 have their ends bent inwardly facing each other. The poles are of sheet metal, much longer than they are wide and much wider than they are thick, and the total area confronting the armature at the ends of the poles 326 and 327 is an area equal to the width times the thickness. As may be seen, only one end of the armature 31 actually touches the poles but the other end comes relatively close.

In the embodiment in FIG. 12 the ends of the poles 426 and 427 are inwardly bent portions, but these inwardly bent portions are not at the very ends of the poles. The armature I31 has outwardly extending knobs at its ends to that only a relatively small area makes contact with the poles, thus limiting the holding force.

In FIG. 11 the armature 231 is somewhat more blunt than the armature 31 in FIG. so that the surfaces 231a-231d do not come flush against the poles 26 and 27. This means that the armature pivots to an angle somewhat smaller than the angle between any of the faces 231a231d and a line drawn along the axis of the armature from the end 231N through the pivot axle 29 to the other end 2318.

In the embodiment on FIG. 13 the same type of armature 31 is used as in some of the earlier embodiments, but each of the poles 526 and 527 has two bumps 526a and 526b and 527a and S271; positioned to make contact with the ends of the armature 31.

v In FIGS. 14 and 15 the armatures 331 have rounded ends concentric with the pivot axis. In FIG. 14 this rounded-end armature pivots between straight poles 26 and 27 to a position of minimum reluctance. The magnetic efficiency is made even greater in the embodiment of FIG. 15 where the poles 626 and 627 are bent to form partially circular surfaces concentric with the pivot axis of the armature 331.

The modification in FIGS. 16 and 17 includes many components identical with the embodiment in FIGS. 1 and 2 and such components have been given the same reference numerals and need not be further described. The embodiment in FIGS. 16 and 17 differs from that in FIGS. 1 and 2 in the arrangement of the permanent magnet, the stator poles, the nonmagnetic indicating number, and the movable resilient arms.

The magnet 431 in FIG. 16 is relatively slightly more blunt than the magnet 31 in FIG. 1 but has the same general con figuration with tapering sides 431a and 431b at one end and 4310 and 431d at the other end. At the very tip of the magnet 431 the magnetic poles 431N and 4315 are squared off. The ferromagnetically soft stator poles 726 and 727 are displaced slightly inwardly at their tips 726a and 727a so that the tip 431N of the magnet strikes either the pole portion 726a or 727a depending upon whether the magnet is in one or the other of its end positions. It should be understood that the magnet 431 could be reversed with the south magnetic pole at the end identified by reference numeral 431N and the north magnetic pole at the end identified by reference numeral 431$. The only part of the magnet 431 that actually touches the pole portions 726a and 727a has a very limited area and does not interfere with reversal of the position of the magnet by means of a field produced by current in the appropriate coil 22 or 23.

The resilient wires that form the movable contacts to engage the fixed contacts M and 37 are indicated by reference numerals 233 and 236, and, as may be seen, these arms are bent inwardly slightly more than the arms 33 and 36 in the embodiment of FIG. 1. However, the outer, or free, ends of the arms 233 and 236 are bent outwardly so that they rub slightly in making contact with the fixed contacts 34 and 37, respectively, thereby keeping these contacts clean to maintain the lowest possible impedance. In order to engage the bent-out ends of the arms 233 and 236 properly, the downwardlytumed flange 3320 on the nonmagnetic member 332 maybe required to have a slightly larger included angle as the flange 32 in FIG. 1.

As may be seen in FIG. 17, the end 727a of the 727 and the corresponding end of the pole 726, is shaped so that it may be soldered directly to a metallized portion on the surface of the plate 21 for better heat conduction from the coils 22 and 23. This soldering of the pole portion 727b can be done simultaneously with or separately from the soldering of other components to the plate 21, which is preferably aceramic plate I with printed wiring thereon.

While this invention has been described in tenns of specific embodiments, it will be recognized by those skilled in the art that modifications may be made therein without departing from the true scope of the invention as defined in the following claims.

lclaim:

1. A microminiature electrical indicator comprising first and second coils; a ferromagnetically soft core for said coils; first and second ferromagnetically soft pole pieces extending in substantially the same direction from opposite ends of said core and spaced apart from each other; a permanent magnet pivotally mounted between said pole pieces; an indicator member attached to said magnet to pivot therewith and comprising an indicating surface section, said indicator member comprising first and second abutment surfaces; first and second switches each comprising an actuator arm in the path of one of said abutment surfaces, respectively, and a relatively stationary contact located adjacent to one of said actuator arms to be engaged thereby; actuating circuit means connecting said first and second switches to said first and second coils, respectively, whereby said switches alternately close an actuating circuit for said first coil and open an actuating circuit for said second coil when said second switch is closed and close said actuating circuit for said second coil and open said actuating circuit for said first coil when said first switch is closed, whereby energizing the closed one of said actuating circuits will energize the one of said coils and thereby energize said pole pieces to draw said magnet to its opposite locating to close the other of said switches and thereby to close the other of said actuating circuits while opening the energized actuator circuit to halt current flow therethrough', and a housing comprising means to view said indicating surface section.

2. The indicator of claim 1 in which said indicator member comprises a substantially fiat surface section and a downturned end portion and said abutment surfaces comprise opposite edges of said downturned portion.

3. The indicator of claim 2 in which said fiat portion of said indicator member substantially covers one surface of said magnet and comprises, in addition, a pair of downturned stop members, one of said stop members on each side of said magnet near one end of said magnet.

4. The indicator of claim 2 in which both ends of said magnet are defined by surfaces tapering to points at each end of said magnet, said surfaces being substantially parallel to said pole pieces in each extreme position of said magnet.

5. The indicator of claim 2 in which said housing comprises two view windows, one of said windows being at one end of said housing and the other of said windows being at one side of said housing perpendicular to the axis on which said magnet pivots, and said indicating surface section comprises first and second painted portions on said downturned portion adjacent to said first window whereby substantially only one color will be visible through said first window when said magnet is in one of its end position and substantially only the other color is visible through said end window when said magnet is in the other of its end positions, said indicating surface section also comprising first and second colored portions of said fiat portion adjacent to said second window whereby only said first color will be visible through said second window when said magnet is in one of its end positions and only said second color will be visible through said second window when said magnet is in the other of its end positions.

6. A magnetically operated indicator comprising: coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil means to be magnetically energized thereby when a current flows in said coil means; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a net current flows in one direction in said coil means and to align itself in a second end position with respect to said poles when a net current flows in the opposite direction in said coil means, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an actuating surface controlled by said armature; electrical contact points near said armature to be actuated by said actuating surface in both of said end positions of said armature; first and second terminals connected, respectively, to said first and second coils to receive energizing currents, said terminals being connected to their respective coils bysaid actuating surface so that current flowing in either of said coils will move said armature to cause said actuating surface to interrupt the circuit to the energizing coil and prevent further current from flowing therethrough while simultaneously completing the circuit to the other of said coils; and an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in.

7. The indicator of claim 6 in which said poles are in the form of strips substantially longer than they are wide and substantially wider than they are thick, and said armature is pivotally mounted substantially midway between said poles with the axis of said armature substantially parallel to the width dimension of each of said poles, and at least a limited area of one end of said armature makes contact with said poles, alternately, in each of said end positions.

8. The indicator of claim 7 in which said poles have outer ends bent inwardly to make contact with one end of said armature in said end positions of said armature.

9. The indicator of claim 8 in which the tips of said outer ends of said poles point substantially directly toward each other.

10. The indicator of claim 8 in which the tips of said outer ends of said poles are bent back away from a direction facing each other.

11. The indicator of claim 8 comprising, in addition: a dimple formed in each of said poles in the region thereof to. make contact with the other end of said armature.

12. The indicator of claim 7 in which said armature has substantially wedge-shaped ends and opposing surfaces of said wedge-shaped ends extend substantially parallel to adjacent surfaces of said poles when said armature is in said end positions.

13. The indicator of claim 7 in which said armature has a projection on each side thereof and said projections comprise said limited area that makes contact with said poles.

14. The indicator of claim 6 in which said armature comprises rounded ends substantially concentric with the axis of said armature and having a radius slightly less than the distance between said poles in the region of said armature.

15. The indicator of claim 14 in which said poles are strips of ferromagnetically soft steel substantially longer than they are wide and substantially wider than they are thick and are bent to form partially circular portions substantially concentric to the axis of said armature.

16. The indicator of claim 6 comprising, in addition: an actuating member attached to said armature to move therewith and engaging said indicating member to move said indicating member between first and second indicating positions.

17. The indicator of claim 16 in which said indicating member comprises a pivotal support pivoting about an axis substantially perpendicular to the axis of said armature.

18. The indicator of claim 17 in which said indicating member comprises edges defining a substantially radial slot and said actuating member engages said slot in a portion thereof radially spaced from the axis of said indicating member.

19. The indicator of claim 6 in which said coil means comprises two solenoid coils wound upon an axis substantially perpendicular to the axis of said armature.

20. An electrical indicator comprising: first and second coils; first and second ferromagnetically soft pole pieces spaced apart from each other and magnetically linked with said coils; an armature comprising a permanently magnetized member movably mounted to be attracted by said pole pieces, an indicating surface section, and first and second actuator surfaces; first and second switches each comprising one arm in the path of one of said actuator surfaces, respectively; electrical circuit means connected to said first and second switches and to said first and second coils whereby said first coil is energizable when said first switch is closed and said second coil is energizable when said second switch is closed, said first coil being magnetically linked to said pole pieces so that when said first coil is energized it produces a magnetic field in said pole pieces to move said armature to open said first switch and to close said second switch, said second coil being magnetically linked to said pole pieces so that when said second coil is energized it produces a magnetic field in said pole pieces to move said armature in the reverse direction to move said actuator surfaces to open said second switch and to close said first switch; and a housing comprising means to view said indicating surface section.

21. The indicator of claim 20 in which said indicator surface section comprises a disc attached to said armature to rotate therewith.

22. The indicator of claim 21 in which said disc has an axial extension along one portion of its periphery and the edges of said axial extension form said actuator surfaces.

23. The indicator of claim 22in which said one arm of each of said switches is a movable arm positioned to be moved by said actuator surfaces and each of said switches comprises, in

addition, a relatively stationary contact located adjacent to its said movable arm to be engaged thereby'to close the respective switch.

24. The indicator of claim 23 in-which each of said movable arms comprises a pair of elongated resilient numbers connected together at one end and engageable by said abutment surfaces at the other end.

25. The indicator of claim 22 in which said axial extension is a portion of a circular cylinder.

26. The indicator of claim 22 in which said axial extension comprises two flat portions making an obtuse angle with each other and the radially outward surface of one of said portions is colored differently than the radially outwardly facing surface of the other of said portions and said housing comprises a window facing said portions and through which only one of said portions at atime may be viewed.

27. The indieator'of claim 20 in which said actuator surfaces are conductive portions of a surface of said indicator member and said one arm of each of said switches bears against said surface of said indicating member to engage, alternately, said actuator surfaces.

28. The electrical indicator of claim 20 in which said electrical circuit means comprises first and second unidirectionally conductive elements connected together so that only one of said unidirectionally conductive elements can conduct at a time, said first and second switches being connected in series with said first and second unidirectionally conductive elements and with said first and second coils, respectively; and an additional circuit means connected to both of said unidirectionally conductive devices to render them alternately conductive in accordance with appli electrical signals, whereby when said first switch is closed said first unidirectionally conductive device can be made conductive to energize said first coil to produce a magnetic field to move said armature to open said first switch and close said second switch and when said second switch isclosed said second unidirectionally conductive device can bemade conductive to energize said second coil to produce a magnetic field of reverse polarity to move said armature in the reverse direction so as to close said second switch and open said first switch.

29. A magnetically operated indicator comprising: solenoid coil means comprising first and second coils and having two ends; a pair of spaced poles magnetically linked to opposite ends of said coil means to be magnetically energized thereby when a current flows in said coil means, each of said poles comprising a strip of ferromagnetically soft material extending substantially parallel to each other and spacedapart over a portion of their length by a first distance and having their ends remote fr )m said coil means offset with respect to said portion so that said ends of said poles are spaced closer to each other than said portion; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a current flows in one direction in said first coil and to align itself in a second end position with respect to said poles when a curr'e ii't cflows in the opposite direction in said second coil, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in; and switch means engaged by said armature in said end positions and electrically connected in series circuit with said coils to open the circuit to said first coil when said armature is in said first end position and to open the circuit to said second coil when said armature is in said second end position.

30. The indicator of claim 29 in which said magnet is elongated and has symmetrical opposite ends formed with sides tapering toward a chisel point and with a fiat area of dimensions small compared to the dimensions of said sides at the extremity of at least one end of said magnet.

31. The indicator of claim 30 in which the spacing between said outer ends of said poles is less than the overall length of said armature and greater than the width of said armature whereby one end of said armature makes contact with said ends of said poles, alternately, in the region of said armature between one of said sides and the flat surface at said end.

32. A magnetically operated indicator comprising: coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil to be magnetically energized thereby when a current flows in said coil means; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a current flows in one direction in said first coil and to align itself in a second end position with respect to said poles when a current flows in the opposite direction in said second coil, the permanent magnetic field of said arma' ture having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in; and first and second switches comprising first and second resilient wires extending substantially parallel to said poles and on opposite sides of said armature and mounted adjacent said coil means with the free ends of said wires adjacent the ends of said poles remote from said coil means, a pair of fixed rigid conductors located adjacent said free ends of said wire with said wires resiliently biased thereagainst, the end portions of said wires bearing on said fixed conductors being bent outwardly to rub against said conductors, said indicating member having means rigidly attached to it to rotate back and forth with it, the outennost ends of said wires extending into the path of motion of said last named means to be engaged thereby to displace said first and second wires, alternately, from contact with said fixed conductors, said first and second switches being electrically connected in series with said first and second coils, respectively, whereby said first switch opens the circuit to said first coil when said armature is in its first end position and said second switch opens the circuit to said second coil when said armature is in its second end position.

33. A magnetically operated indicator comprising: an insulating support member; conductive areas on said member; coil means comprising first and second coils; a pair of spaced l'er romagnetically soft poles magnetically linked to said coil to be magnetically energized thereby when a current flows in said coil means, said poles being soldered to said conductive areas adjacent said coil means to conduct heat from said coil means to said member; a permanently magnetized armature pivotally magnetized to align itself in a first end position with respect to said poles when a net current flows in one direction in said coil means and to align itself in a second end position with respect to said poles when a net current flows in the opposite direction in said coil means, the permanent magnetic field of said arma-. ture having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature rs m; a switch means connected as a double-pole, single-throw switch in series with said first and second coils to permit only one of said coils to be energized at a time to attract said armature, said switch means being physically located to be actuated by said armature to disconnect the energized one of said coils and to connect the other of said coils as said armature moves in response to the attraction of one coil.

34. The indicator of claim 6 in which said indicating member comprises a flat surface portion substantially perpendicular to the axis of said pivotally mounted armature, a downturned portion substantially parallel to said axis, and areas of first and second colors located both on said flat surface portion and on said downturned portion, said indicator comprising, in addition: a housing comprising an end having a first view window and a side substantially perpendicular to said axis and comprising a second view window, said areas of first and second colors on said downtumed portion being adjacent to said first window whereby substantially only said first color will be visible through said first window when said armature is in one of its end positions and substantially only said second color is visible through said first window when said armature is in the other of its end positions, said areas of first and second colors on said flat surface portion being adjacent to said second window, whereby only said first color will be visible through said second window when said armature is in said one of its end portions and only said second color will be visible through said second window when said armature is in said other of its end positions.

35. A magnetically operated indicator comprising: coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil means to be magnetically energized thereby when a current flows in said coil means; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a current flows in one direction in said first coil and to align itself in a second end position with respect to said poles when a current flows in the opposite direction in said second coil, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no current flows in said coil means; an indicating member rigidly connected to said armature to move therewith comprising a flat surface portion substantially perpendicular to the axis to said armature, a downturned portion substantially parallel to said axis, and areas of first and second colors located both on said flat surface portion and on said downturned portion; a housing comprising an end having a first view window, and a side substantially perpendicular to said axis and comprising a second view window, said areas of first and second colors on said downturned portion being adjacent to said first window whereby substantially only said first color will be visible through said first window when said armature is in said first end position and substantially only said second color is visible through said first window when said armature is in said second end positions, said areas of first and second colors on said flat surface portion being adjacent to said second window, whereby only said first color will be visible through said second window when said armature is in said first end position and only said second color will be visible through said second window when said armature is in said second end position; a switch means connected as a double-pole, single-throw switch in series with said first and second coils to permit only one of said coils to be energized at a time to attract said armature, said switch means being physically located to be actuated by said armature to disconnect the energized one of said coils and to connect the other of said coils as said armature moves in response to the attraction of said one coil. 

1. A microminiature electrical indicator comprising first and second coils; a ferromagnetically soft core for said coils; first and second ferromagnetically soft pole pieces extending in substantially the same direction from opposite ends of said core and spaced apart from each other; a permanent magnet pivotally mounted between said pole pieces; an indicator member attached to said magnet to pivot therewith and comprising an indicating surface section, said indicator member comprising first and second abutment surfaces; first and second switches each comprising an actuator arm in the path of one of said abutment surfaces, respectively, and a relatively stationary contact located adjacent to one of said actuator arms to be engaged thereby; actuating circuit means connecting said first and second switches to said first and second coils, respectively, whereby said switches alternately close an actuating circuit for said first coil and open an actuating circuit for said second coil when said second switch is closed and close said actuating circuit for said second coil and open said actuating circuit for said first coil when said first switch is closed, whereby energizing the closed one of said actuating circuits will energize the one of said coils and thereby energize said pole pieces to draw said magnet to its opposite locating to close the other of said switches and thereby to close the other of said actuating circuits while opening the energized actuator circuit to halt current flow therethrough; and a housing comprising means to view said indicating surface section.
 2. The indicator of claim 1 in which said indicator member comprises a substantially flat surface section and a downturned end portion and said abutment surfaces comprise opposite edges of said downturned portion.
 3. The indicator of claim 2 in which said flat portion of said indicator member substantially covers one surface of said magnet and comprises, in addition, a pair of downturned stop members, one of said stop members on each side of said magnet near one end of said magnet.
 4. The indicator of claim 2 in which both ends of said magnet are defined by surfaces tapering to points at each end of said magnet, said surfaces being substantially parallel to said pole pieces in each extreme position of said magnet.
 5. The indicator of claim 2 in which said housing comprises two view windows, one of said windows being at one end of said housing and the other of said windows being at one side of said housing perpendicular to the axis on which said magnet pivots, and said indicating surface section comprises first and second painted portions on said downturned portion adjacent to said first window whereby substantially only one color will be visible through said first window when said magnet is in one of its end position and substantially only the other color is visible through said end window when said magnet is in the other of its end positions, said indicating surface section also comprising first and second colored portions of said flat portion adjacent to said second window whereby only said first color will be visible through said second window when said magnet is in one of its end positions and only said second color will be visible through said second window when said magnet is in the other of its end positions.
 6. A magnetically operated indicator comprising: coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil means to be magnetically energized thereby when a current flows in said coil means; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a net current flows in one direction in said coil means and to align itself in a second end position with rEspect to said poles when a net current flows in the opposite direction in said coil means, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an actuating surface controlled by said armature; electrical contact points near said armature to be actuated by said actuating surface in both of said end positions of said armature; first and second terminals connected, respectively, to said first and second coils to receive energizing currents, said terminals being connected to their respective coils by said actuating surface so that current flowing in either of said coils will move said armature to cause said actuating surface to interrupt the circuit to the energizing coil and prevent further current from flowing therethrough while simultaneously completing the circuit to the other of said coils; and an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in.
 7. The indicator of claim 6 in which said poles are in the form of strips substantially longer than they are wide and substantially wider than they are thick, and said armature is pivotally mounted substantially midway between said poles with the axis of said armature substantially parallel to the width dimension of each of said poles, and at least a limited area of one end of said armature makes contact with said poles, alternately, in each of said end positions.
 8. The indicator of claim 7 in which said poles have outer ends bent inwardly to make contact with one end of said armature in said end positions of said armature.
 9. The indicator of claim 8 in which the tips of said outer ends of said poles point substantially directly toward each other.
 10. The indicator of claim 8 in which the tips of said outer ends of said poles are bent back away from a direction facing each other.
 11. The indicator of claim 8 comprising, in addition: a dimple formed in each of said poles in the region thereof to make contact with the other end of said armature.
 12. The indicator of claim 7 in which said armature has substantially wedge-shaped ends and opposing surfaces of said wedge-shaped ends extend substantially parallel to adjacent surfaces of said poles when said armature is in said end positions.
 13. The indicator of claim 7 in which said armature has a projection on each side thereof and said projections comprise said limited area that makes contact with said poles.
 14. The indicator of claim 6 in which said armature comprises rounded ends substantially concentric with the axis of said armature and having a radius slightly less than the distance between said poles in the region of said armature.
 15. The indicator of claim 14 in which said poles are strips of ferromagnetically soft steel substantially longer than they are wide and substantially wider than they are thick and are bent to form partially circular portions substantially concentric to the axis of said armature.
 16. The indicator of claim 6 comprising, in addition: an actuating member attached to said armature to move therewith and engaging said indicating member to move said indicating member between first and second indicating positions.
 17. The indicator of claim 16 in which said indicating member comprises a pivotal support pivoting about an axis substantially perpendicular to the axis of said armature.
 18. The indicator of claim 17 in which said indicating member comprises edges defining a substantially radial slot and said actuating member engages said slot in a portion thereof radially spaced from the axis of said indicating member.
 19. The indicator of claim 6 in which said coil means comprises two solenoid coils wound upon an axis substantially perpendicular to the axis of said armature.
 20. An electrical indicator comprising: first and second coils; first and second ferromagnetically soft pole pieces spaced apart fRom each other and magnetically linked with said coils; an armature comprising a permanently magnetized member movably mounted to be attracted by said pole pieces, an indicating surface section, and first and second actuator surfaces; first and second switches each comprising one arm in the path of one of said actuator surfaces, respectively; electrical circuit means connected to said first and second switches and to said first and second coils whereby said first coil is energizable when said first switch is closed and said second coil is energizable when said second switch is closed, said first coil being magnetically linked to said pole pieces so that when said first coil is energized it produces a magnetic field in said pole pieces to move said armature to open said first switch and to close said second switch, said second coil being magnetically linked to said pole pieces so that when said second coil is energized it produces a magnetic field in said pole pieces to move said armature in the reverse direction to move said actuator surfaces to open said second switch and to close said first switch; and a housing comprising means to view said indicating surface section.
 21. The indicator of claim 20 in which said indicator surface section comprises a disc attached to said armature to rotate therewith.
 22. The indicator of claim 21 in which said disc has an axial extension along one portion of its periphery and the edges of said axial extension form said actuator surfaces.
 23. The indicator of claim 22 in which said one arm of each of said switches is a movable arm positioned to be moved by said actuator surfaces and each of said switches comprises, in addition, a relatively stationary contact located adjacent to its said movable arm to be engaged thereby to close the respective switch.
 24. The indicator of claim 23 in which each of said movable arms comprises a pair of elongated resilient numbers connected together at one end and engageable by said abutment surfaces at the other end.
 25. The indicator of claim 22 in which said axial extension is a portion of a circular cylinder.
 26. The indicator of claim 22 in which said axial extension comprises two flat portions making an obtuse angle with each other and the radially outward surface of one of said portions is colored differently than the radially outwardly facing surface of the other of said portions and said housing comprises a window facing said portions and through which only one of said portions at a time may be viewed.
 27. The indicator of claim 20 in which said actuator surfaces are conductive portions of a surface of said indicator member and said one arm of each of said switches bears against said surface of said indicating member to engage, alternately, said actuator surfaces.
 28. The electrical indicator of claim 20 in which said electrical circuit means comprises first and second unidirectionally conductive elements connected together so that only one of said unidirectionally conductive elements can conduct at a time, said first and second switches being connected in series with said first and second unidirectionally conductive elements and with said first and second coils, respectively; and an additional circuit means connected to both of said unidirectionally conductive devices to render them alternately conductive in accordance with applied electrical signals, whereby when said first switch is closed said first unidirectionally conductive device can be made conductive to energize said first coil to produce a magnetic field to move said armature to open said first switch and close said second switch and when said second switch is closed said second unidirectionally conductive device can be made conductive to energize said second coil to produce a magnetic field of reverse polarity to move said armature in the reverse direction so as to close said second switch and open said first switch.
 29. A magnetically operated indicator comprising: solenoid coil means comprising first and secoNd coils and having two ends; a pair of spaced poles magnetically linked to opposite ends of said coil means to be magnetically energized thereby when a current flows in said coil means, each of said poles comprising a strip of ferromagnetically soft material extending substantially parallel to each other and spaced apart over a portion of their length by a first distance and having their ends remote from said coil means offset with respect to said portion so that said ends of said poles are spaced closer to each other than said portion; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a current flows in one direction in said first coil and to align itself in a second end position with respect to said poles when a current flows in the opposite direction in said second coil, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in; and switch means engaged by said armature in said end positions and electrically connected in series circuit with said coils to open the circuit to said first coil when said armature is in said first end position and to open the circuit to said second coil when said armature is in said second end position.
 30. The indicator of claim 29 in which said magnet is elongated and has symmetrical opposite ends formed with sides tapering toward a chisel point and with a flat area of dimensions small compared to the dimensions of said sides at the extremity of at least one end of said magnet.
 31. The indicator of claim 30 in which the spacing between said outer ends of said poles is less than the overall length of said armature and greater than the width of said armature whereby one end of said armature makes contact with said ends of said poles, alternately, in the region of said armature between one of said sides and the flat surface at said end.
 32. A magnetically operated indicator comprising: coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil to be magnetically energized thereby when a current flows in said coil means; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a current flows in one direction in said first coil and to align itself in a second end position with respect to said poles when a current flows in the opposite direction in said second coil, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in; and first and second switches comprising first and second resilient wires extending substantially parallel to said poles and on opposite sides of said armature and mounted adjacent said coil means with the free ends of said wires adjacent the ends of said poles remote from said coil means, a pair of fixed rigid conductors located adjacent said free ends of said wire with said wires resiliently biased thereagainst, the end portions of said wires bearing on said fixed conductors being bent outwardly to rub against said conductors, said indicating member having means rigidly attached to it to rotate back and forth with it, the outermost ends of said wires extending into the path of motion of said last named means to be engaged thereby to displace said first and second wires, alternately, from contact with said fixed conductors, said first and second switches being electrically connected in series with said first and second coils, respectively, whereby said first switch opens the circuit to said first coil when sAid armature is in its first end position and said second switch opens the circuit to said second coil when said armature is in its second end position.
 33. A magnetically operated indicator comprising: an insulating support member; conductive areas on said member; coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil to be magnetically energized thereby when a current flows in said coil means, said poles being soldered to said conductive areas adjacent said coil means to conduct heat from said coil means to said member; a permanently magnetized armature pivotally magnetized to align itself in a first end position with respect to said poles when a net current flows in one direction in said coil means and to align itself in a second end position with respect to said poles when a net current flows in the opposite direction in said coil means, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no net current flows in said coil means; an indicating member connected to said armature to move therewith to indicate at all times which of said end positions said armature is in; a switch means connected as a double-pole, single-throw switch in series with said first and second coils to permit only one of said coils to be energized at a time to attract said armature, said switch means being physically located to be actuated by said armature to disconnect the energized one of said coils and to connect the other of said coils as said armature moves in response to the attraction of one coil.
 34. The indicator of claim 6 in which said indicating member comprises a flat surface portion substantially perpendicular to the axis of said pivotally mounted armature, a downturned portion substantially parallel to said axis, and areas of first and second colors located both on said flat surface portion and on said downturned portion, said indicator comprising, in addition: a housing comprising an end having a first view window and a side substantially perpendicular to said axis and comprising a second view window, said areas of first and second colors on said downturned portion being adjacent to said first window whereby substantially only said first color will be visible through said first window when said armature is in one of its end positions and substantially only said second color is visible through said first window when said armature is in the other of its end positions, said areas of first and second colors on said flat surface portion being adjacent to said second window, whereby only said first color will be visible through said second window when said armature is in said one of its end portions and only said second color will be visible through said second window when said armature is in said other of its end positions.
 35. A magnetically operated indicator comprising: coil means comprising first and second coils; a pair of spaced ferromagnetically soft poles magnetically linked to said coil means to be magnetically energized thereby when a current flows in said coil means; a permanently magnetized armature pivotally mounted to align itself in a first end position with respect to said poles when a current flows in one direction in said first coil and to align itself in a second end position with respect to said poles when a current flows in the opposite direction in said second coil, the permanent magnetic field of said armature having sufficient strength to maintain said armature in either of said end positions when no current flows in said coil means; an indicating member rigidly connected to said armature to move therewith comprising a flat surface portion substantially perpendicular to the axis to said armature, a downturned portion substantially parallel to said axis, and areas of first and second colors located both on said flat surface portion and on said downturned portion; a housing comprising an end having a first View window, and a side substantially perpendicular to said axis and comprising a second view window, said areas of first and second colors on said downturned portion being adjacent to said first window whereby substantially only said first color will be visible through said first window when said armature is in said first end position and substantially only said second color is visible through said first window when said armature is in said second end positions, said areas of first and second colors on said flat surface portion being adjacent to said second window, whereby only said first color will be visible through said second window when said armature is in said first end position and only said second color will be visible through said second window when said armature is in said second end position; a switch means connected as a double-pole, single-throw switch in series with said first and second coils to permit only one of said coils to be energized at a time to attract said armature, said switch means being physically located to be actuated by said armature to disconnect the energized one of said coils and to connect the other of said coils as said armature moves in response to the attraction of said one coil. 